That makes sense, butt fusion probably only requires the two ends to match, so SIDR instead of SDR or DR would be no problem. Back when I was looking at costs for butt fusion iron and jig it was way more expensive than for the socket fusion iron and adapters. Though socket fusion equipment was expensive also, it could be gotten for half of butt fusion equipment.
On ebay there is a good chance that you could buy a used McElroy butt end weld jig with heater and face cutting tool at a good price. When I was watching them they were less than $500 and lower. If I were going to do more than one loop I would have purchased one.
I paid over $800 to have the pipe fused at the house and paid earlier to have loop joints welded out in the field. I should have done it all in one step and paid less, but that takes a lot of preplanning. With renting a trencher I focused on the outside loop first, but wasn't ready for inside since I didn't have the surge volume device that I wanted identified and purchased yet.
Thank you for sharing that photo of your basement wall perforations, nice setup! Please tell me some details about your configuration. You mentioned you have a three ton heat pump. You said you have "3 loops of 1" srd 800' long", are those horizontal loops? Is that 800 feet per loop?
Check out my thread. https://www.geoexchange.org/forum/threads/my-diy-geo-install.6550/ Horizontal loops 800' each. 2400' total for my house. And another 2400' for my shop. Both 3 ton units.